Participants of many sports, including baseball, football, soccer, hockey, tennis, and golf, and their coaches, are often interested in knowing the motion characteristics of the object used in a sport, such as the distance, time of flight, speed, height, spin rate, or curve of thrown, kicked, or batted balls and slapped hockey pucks. Typically, the speed of a moving ball is measured using a Doppler radar system. Doppler radar systems determine a moving ball's speed by analyzing radar beams reflected off the ball. Although accurate, these systems are expensive and normally cannot be operated by the athlete whose toss or hit is being measured. For these reasons, systems of this type are generally restricted to organized sport teams. Also, Doppler radar systems are not able to measure the spin rate of the ball of interest. Spin rate information is useful, for example, in optimizing a baseball pitcher's curve ball pitching ability.
Several other methods for measuring the motion characteristics of moving objects have been proposed over the years that rely on devices wholly external to the moving object. Another approach to the problem involves placing a measurement device within the moving object. Four such systems are described in U.S. Pat. No. 4,775,948 issued on Oct. 4, 1988 to Dial et al. entitled "Baseball Having Inherent Speed-Measuring Capabilities", the '948 patent; U.S. Pat. No. 5,526,326 issued on Jun. 11, 1996 to Fekete et al. entitled "Speed Indicating Ball", the '326 patent; U.S. Pat. No. 5,761,096 issued on Jun. 2, 1998 to Zakutin entitled "Speed Sensing Projectile", the '096 patent; and U.S. Pat. No. 5,779,576 issued on Jul. 14, 1998 to Smith, III et al. entitled "Throw Measuring Football", the '576 patent.
The '948 and '096 patents involve detecting the time of a baseball flight using devices internal to the ball that respond to the linear acceleration at the beginning of a toss and/or at the end when the ball is caught. The '948 patent also proposes using a button on the surface of the ball to detect when the ball is released by the pitcher. The '096 patent discloses a projectile, such as a baseball, having an inertial switch that opens and closes in response to linear accelerations. The inertial switch is the subject of U.S. Pat. No. 5,786,553 issued on Jul. 28, 1998 to Zakutin entitled "Inertial Switch." An electronic timer internal to the ball measures the ball's time between acceleration events as the time of flight over a measured distance, and on that basis determines the ball's speed. The speed is then displayed on the surface of the ball via a liquid crystal display.
The '326 patent suggests that a more economical and durable method of accomplishing the same task is met by using mechanical means internal to a ball for determining time of flight and speed. The ball is wound up like a wind-up clock and unwinds when released during a toss. The amount that it unwinds indicates the time-of-flight and, over a known distance, also the ball's speed.
The '576 patent discloses an accelerometer in cooperation with a microprocessor within a projectile, such as a football. The degree of linear acceleration experienced at the beginning of a toss is measured and used to estimate trajectory statistics. A liquid crystal display on the surface of the football allows flight characteristics calculated by the microprocessor to be displayed.
U.S. Pat. No. 5,497,704 issued to Kurschner, et al., on Mar. 12, 1996 entitled "Multifunctional Magnetic Fuze", describes a method for determining the number of rotations of a firing weapon projectile using the earth's magnetic field. In patent '704, however, no means is provided for displaying to the user of the device the measured spin rate of the projectile. The number of projectile rotations is measured to count down to projectile detonation. In addition, in patent '704 the measurement of spin rate is not begun in response to the detection of spin or launch by circuitry wholly internal to the projectile, measurement is begun as a result of interaction with the projectile's firing barrel. Also in patent '704, the firing barrel transmits a signal to the projectile as it is leaving the barrel. This signal initiates the projectile's spin metering process. Also in patent '704, the projectile's muzzle velocity is computed based on the barrel pitch constant of the firing weapon and the measured spin rate of the projectile.
It is thus apparent that there is a need in the art for an improved measuring method or apparatus which does not significantly or materially alter the moving object's physical characteristics or flight performance, has low power requirements, is inexpensive and durable, is applicable to many different types of sports equipment and other movable objects, measures many different motion characteristics including spin rate, and is operable by the person doing the throwing, kicking, or hitting. The present invention meets these and other needs in the art.
This application is a continuation-in-part of application Ser. No. 09/346,003 of Dave Marinelli filed on Jul. 1, 1999 entitled "A Speed, Spin Rate, and Curve Measuring Device Using Multiple Sensor Types," which is incorporated herein by reference for all that is disclosed and taught therein. Application Ser. No. application Ser. No. 09/007,241 of Dave Marinelli.